This invention relates generally to pipelines and more particularly concerns the storage, delivery and spooling of pipelines which have been preassembled for laying at a remote location, such as underwater pipelines used in off-shore well production systems.
The first off-shore pipeline was laid in the Gulf of Mexico in 1954 using conventional land-based pipe laying methods at sea. As seen in FIG. 1, stalks K are formed by on-shore welding of two or three sections of pipe P and coating and testing the welds. The stalks K are then loaded onto relatively small boats B for delivery to an at-sea navigable site such as a barge or ship. There the stalks K are welded end-to-end to each other in a horizontal orientation and these new welds coated and tested for release to the sea, one stalk at a time, in what is a tediously slow “S-lay” process, “S” describing the path of the pipeline as it leaves the floating site. This at-sea application of the land-based conventional method remains in use today but, primarily because of increased possibilities of pipeline failure resulting from the “S-lay” pipeline release path, it is generally used only for laying pipe in shallower water less than 1000′ deep. Assuming the water depth is shallow, the at-sea barge or ship may also be relatively small because the length and weight of pipe on board at any given time is minimal. But, the stalk joining time can take from 20 minutes to 2 hours per joint, depending on materials, dimensions, welding procedures, inter-pass temperatures, coatings, liners, pipe-in-pipe applications and related considerations.
In the late 1960s, spool-based pipeline systems came into use. According to the spool-based method, looking at FIG. 2, the stalks K or sections of pipe P are delivered to an on-shore facility near the docking point where they are individually joined and reeled onto a ship-board spool S. This is also a tediously slow process because reeling must stop at each joint while the stalks K or sections of pipe P are welded, coated and tested. The sections of pipe P are typically in short lengths, perhaps 40′, and the stalks K somewhat longer, perhaps as much as half a mile long. In one recent case, a 1.25 mile long linear site was specially built at a cost of approximately $30,000,000. The reeled pipelines L are often as much as six miles long or more, depending on the pipe diameter and wall thickness. As a result, considerably larger and more expensive vessels V are required to transport the spool S to the at-sea pipeline laying location. Moreover, the spool-carrying vessel V is designed and its supporting equipment positioned so that the completed pipeline L will be dispensed over the stern of the vessel V as it travels. As a result, these spool-carrying vessels V also require stern loading. Therefore, they must be moored substantially stern-on in the harbor to receive the pipeline L from the welding facility axially in the direction of the keel which is transverse to the reel rotational axis. The resulting in-harbor time and space requirements for the vessel V make it generally difficult and sometimes impossible for conventional harbors to accommodate the spool-based process. Even when the harbor can accommodate the vessel V, the method essentially transfers the lengthy at-sea welding and coating process to the seashore, so that an extremely expensive vessel V, as well as related harbor facilities, are operationally idle for days as pipeline is being welded, coated and reeled. On many projects, time spent in harbor can be as much as 10 days. Over the course of a pipe lay season, a reel lay vessel V may spend more than 80 days in harbor reeling stalks of pipe at a cost of approximately $400,000 per day.
In 1993, a “J-lay” variation of the conventional at-sea welding process was put into practice, “J” describing the path of the pipeline as it leaves the floating site. In “J-lay” systems, a tower on the floating site permits the pipe to be welded in vertical orientation. This enables the sea welding process previously limited to use in waters less than 1000′ in depth to be used in waters many thousands of feet in depth but leaves the other above-mentioned conventional process problems unresolved.
Recently, a 2006 publication related to spool-based pipeline reeling suggests that the pipeline be welded and then stored at a land-based facility for future non-stop reeling onto a ship-board spool S. Such a system could reduce the idle time of the vessel V. However, according to the suggested system, as seen in FIG. 3, the pipeline L must be collected and stored on a synchronized train T of bogies driven on an endless circular track. While the train is circular, the pipeline L is spiralled onto the train T. The constant variation of the spiralling pipeline radius is practical only for elastic bending of the pipe. It is also suggested that pipelines could be stacked in layers spaced by timber battens, but only the topmost layer of the stack could be accessed at any time. To transfer the stored pipeline L to a vessel V, the pipeline L, or the topmost pipeline if pipelines are stacked, would be unloaded from the endless track T onto a tangent path for straight-line transfer to a nearby stern-moored vessel V. This combination of preconditions would increase the already existing difficulty in finding geographically and geometrically suitable sites for spool-based operations. A suitable site could be as much as five or more days' vessel run from the pipeline lay area. Increased sailing time would greatly offset any weld time saved by use of the system. The resulting disadvantages more than offset any benefits that might result from use of the bogie train spool-based system.
In a more recently suggested stacked pipeline system, the pipeline would be coiled under itself in circular, concentric circular or spaced semi-circular configurations, as seen in FIGS. 4A-C, respectively. This system eliminates the constantly variable spiral radius of the pipe bend in the track-and-bogie system. However, in each of these configurations, each succeeding coil would lift and support the weight of each and every preceding coil. As with the track-and-bogie system, in-take and out-take to and from the coils would be tangential to the loop and straight line to both the weld station (not shown) and to the stern of the vessel V. The choice of site would be limited to those able to accommodate at least the size of a circular loop having the elastic bending radius of the pipeline L and also to afford a straight line path tangent to the loop and perpendicular to the reel rotational axis of the spool S on the stern-moored vessel V. Stacking identical coils of pipe would require use of the same radius and identical loop path for the entire stack. The weight of the stacked loops would increasingly challenge the integrity of successively lower loops and would make pipe-in-pipe or multiple pipe applications highly impractical. The stacked coils could not accommodate partial radii and, therefore, the pipeline L could not be bent in all possible directions. Pipeline or weld repairs could not be made to the coiled pipeline, nor would it be possible to move a repair point on a coil to a designated repair location without unwinding and/or breaking a welded joint. Stacking is proposed to be accomplished by insertion of a new lowermost coil between stack-supporting rollers and the next lowermost coil to lift the already stacked coils as the pipeline is pushed under the bottom of the stack, an impractical if not impossible task. The order of loadout from a looped stack could not be changed because, once the pipeline was stacked, the lower loops could not be accessed or retrieved until the higher loops were remove from the stack. Even if this order could be changed, pipelines of different diameter L1 and L2 could not be stored in the same stack. For example, a 4″ pipe being pushed under a 10″ pipe would create an unstable condition. Retrieval of the pipeline from the loop would be likely to damage the stack-supporting rollers or the pipe because of the weight of the stack. Retrieval of the pipeline from the loop is likely to damage rollers used to guide the pipeline or the pipe because one section of the pipeline would want to elastically turn against the last guiding roller while the other elastically bent sections were holding the roller in place. As the pipeline relaxes from the loop, it would want to describe a curve of increasing radius and either force its way off the exit rollers or, if restrained, cross over at the loop exit so that the top layer would be forced off the inside of the loop. Some of the loops would occasionally want to fall off the supporting rollers, especially if there were only one guiding roller. This is so because, in practice, line pipes have quite different strengths from batch to batch and would push the pipeline off the rollers, especially when going from bent to straight and vice versa. The stacked loops might push down on the bottom coil sufficiently to force it off the roller system or into a tangle or might put sufficient load on the bottom and intermediate coils to eventually cause damage to the coatings or field joints on the bottom coil as it crosses the supporting rollers. Moreover, stacked loops would eventually buckle the pipeline between the welding station and the loop as the tensioner pushes the stacked load. Any vertical deviations in a coil would be magnified in successive coils so three dimensional circumnavigation of any obstacles in the coil path would be impractical. The stacked coil roller support and guide structure would require such considerable strength to handle its multiple loops that the system would lack portability. Thus, the stacked coil variation of the bogie train spiral has concomitant disadvantages which would mitigate greatly against its use in a spool-based system.
Thus, despite the efforts to devise a more practical method and system, the present state of undersea pipeline technology is limited to “S-lay” and “J-lay” weld-at-sea methods or seashore weld-and-reel methods. Both are relatively inefficient and expensive and, with respect to off-shore oil production applications, add significantly to an already burdensome consumer cost.
It is, therefore, an object of this invention to provide a method for storing, delivering and spooling pipelines which speeds up spooling times. Another object of this invention is to provide a method for storing, delivering and spooling pipelines which reduces the occurrences of disruption during the spooling operation. Still another object of this invention is to provide a method for storing, delivering and spooling pipelines which reduces in-harbor idle time for pipe-lay vessels. A further object of this invention is to provide a method for storing, delivering and spooling pipelines which reduces the risk of weld failures. Yet another object of this invention is to provide a method for storing, delivering and spooling pipelines which gives access to a greater choice of spool-base sites. It is also an object of this invention to provide a method for storing, delivering and spooling pipelines which eliminates the need for stem-on or angled mooring of spooling vessels. A further object of this invention is to provide a method for storing, delivering and spooling pipelines which makes complex jointing systems, such as pipe-in-pipe and high Cr content, more attractive for reel lay. Another object of this invention is to provide a method for storing, delivering and spooling pipelines which does not require that a stored pipeline come into spiralled or coiled contact with itself or other pipelines. Still another object of this invention is to provide a method for storing, delivering and spooling pipelines which utilizes a discrete point-to-point storage path which the pipeline traces. A further object of this invention is to provide a method for storing, delivering and spooling pipelines which is capable of including multiple radii in a pipeline storage, delivery or spooling-path. Yet another object of this invention is to provide a method for storing, delivering and spooling pipelines which can accommodate partial radii permitting the pipeline to be bent in all available directions. It is also an object of this invention to provide a method for storing, delivering and spooling pipelines which permits pipeline or weld repairs to be performed anywhere on the pipeline storage path. Another object of this invention is to provide a method for storing, delivering and spooling pipelines which permits movement of a repair point on a pipeline storage path to a repair location. Yet another object of this invention is to provide a method for storing, delivering and spooling pipelines which permits coupling a traditional spoolbase or straight rack to its pipeline storage path. It is also an object of this invention to provide a method for storing, delivering and spooling pipelines which enables selective retrieval of pipeline portions from storage. Another object of this invention is to provide a method for storing, delivering and spooling pipelines which allows various diameter pipelines to be stored end-to-end and retrieved as desired. Still another object of this invention is to provide a method for storing, delivering and spooling pipelines which supports the stored pipeline directly on rollers. A further object of this invention is to provide a method for storing, delivering and spooling pipelines which is tolerant of mismatched pipe strengths on a joint-by-joint basis. Yet another object of this invention is to provide a method for storing, delivering and spooling pipelines which allows the stored pipeline to circumnavigate obstacles on the storage site or along the delivery route in three dimensions. And it is an object of this invention to provide a method for storing, delivering and spooling pipelines which enables use of portable pipeline storage, delivery and spooling path components.